CCAMLR

This paper presents a simultaneous system-of-equations approach to modeling age-structured populations using trawl survey age/size frequency data. The analysis builds upon a Ricker spawner-recruit structure and provides a cohort-based estimation method that retains the underlying dynamic properties of a delay-difference model. The framework shares a common spawner-recruit function across age-class equations. This exploits the commonality among cohort members and serves as an instrumental variable, lessening the effect of measurement errors in estimation. The dynamic features of the underlying age-structured population are retained through age-specific net survivability and growth parameters that link age-classes. The technique uses multiple observations on a cohort to further mitigate the effect of measurement error and improve overall estimation efficiency. A seemingly unrelated regression estimation method is required to address contemporaneous correlation of errors across age-classes. This framework is applied to trawl survey data for adult male Alaskan king crab, Paralithodes camtschaticus.

In order to assess the abundance of the red crab Geryon quinquedens, two otter-trawl cruises were undertaken in July and September 1978, on the continental slope off South West Africa. A bimodal frequency distribution of female crabs was evident with modal sizes at 7.7 cm and 8.7 cm carapace width, whereas the mode for males was at 11.2 cm. In general. larger animals tended to inhabit shallower water, i.e. size is inversely related to depth. Females preferred shallower water than males. Shell states indicated that males were predominantly in the inter-moult stage while most females were either approaching or had recently completed the moult. From morphometric relationships, it was calculated that, in processing the live material to a cooked frozen product, red crab is subject to a mass loss of about 54 per cent. Analysis of stomach contents by volume showed that only 12 per cent of male stomachs contained 5 per cent or more food and 2 per cent of female stomachs exceeded the 5-per-cent level. Highest crab densities occurred at depths of 472-849 m, whereas unusually high concentrations were encountered during two trawls at water depths of 549 and 590 m. The red crab survives at extremely low levels of dissolved oxygen and tolerates a temperature range of more than 7°C.

The stone crab Lithodes murrayi was exploited briefly off South West Africa between November 1979 and April 1980, the fishery being terminated when the catch per unit effort fell to an uneconomic level. The extent of the L. murrayi grounds is examined on the basis of catch-per-unit-effort data. The species is largely confined to a bathymetric corridor of 500–700 m off South West Africa. Prior to commercial fishing, there was a densely populated region between 24°00'S and 24°40'S, although the crabs were present in small numbers over a much larger area. Over 90 per cent of the fishing effort was applied in this area of high concentration, accounting for almost 95 per cent by mass of the total catch. Although the catch rate declined, the mean size of exploitable crabs and of undersize crabs stayed virtually constant. Some morphometric relationships and a factor for converting processed crab section mass to whole crab mass have been calculated.

A quantitative analysis was carried out to estimate the maximum sustainable yield of blue crab distributed around the waters of Korea and in the East China Sea without using fishing effort data, fitting monthly catch data to a modified surplus production model.
The maximum sustainable yield of this fish stock was estimated to be about 22,400 tonnes per year and Fmsy to be 0.95.